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kandyflip445 · 02-03-2003, 12:09 AM

ABS

mrmephistopheles stated how the ECU determines when the ABS comes on. Wheel speed sensors(the magnetic sensor) are at ALL wheels(from what I've seen. what good would it be if 3 of your wheels were good and one locked up on ice and to started to pulse?). They detect when to make the ABS operate.

Normal braking- When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the normally open inlet ports of the Hydraulic Control Unit(HCU). The prake fluid travels through the HCY, ininterrupted, andout the outlet ports of hte HCY. Fluid then travels to the braking units just like in a normal system.

Anti-Lock Mode- If the driver gets into a situation where the brakes are applied hard enough to cause a wheel to lock u, the ECU will send signals to the HCU. The HCU will use these signals to prevent wheel lockup from occurring. Although the exact method the HCU will use to do this will vary between the different ABS systems. the following will occur:

- The ECU will determine what wheel is in danger of lockup. This decision is based on the wheel rotation speed and the deceleration rate of the other wheel(s).

-The ECU will then send an electrical signal to the HCU. This activates the solenoid that controls the isolation/inlet valve for the hydraulic circuit for that wheel. This action cuts off the fluid flow, preventing any more master cylinder hydraulic pressure from reaching the wheel.

-The ECU then looks at the sensor signal from the affected wheel again.

-If the affected wheel is still decelerating too quickly, the ECU will send a signal to the HCU that will open the normally closed dump/outlet valve for that circuit. This dumps any applied pressure from the brake back to the reservoir.

-Once the affected wheel comes back to a speed whick is acceptable to the ECU, the ECU will return the inlet/isolation and dump/outlet valves back to their normal positions. This allows brake fluid to travel to the brake units once again.

-These actions will repeat until the brakes can be applied without risk of lockup. Different traction situations will require more or less cycles of the valves.

02-03-2003, 12:09 AM	#6
kandyflip445 Post Whore! Join Date: Sep 2002 Location: Arden, NC Age: 39 Posts: 4,460 Trader Rating: (1)	ABS mrmephistopheles stated how the ECU determines when the ABS comes on. Wheel speed sensors(the magnetic sensor) are at ALL wheels(from what I've seen. what good would it be if 3 of your wheels were good and one locked up on ice and to started to pulse?). They detect when to make the ABS operate. Normal braking- When the brakes are applied, fluid is forced from the brake master cylinder outlet ports to the normally open inlet ports of the Hydraulic Control Unit(HCU). The prake fluid travels through the HCY, ininterrupted, andout the outlet ports of hte HCY. Fluid then travels to the braking units just like in a normal system. Anti-Lock Mode- If the driver gets into a situation where the brakes are applied hard enough to cause a wheel to lock u, the ECU will send signals to the HCU. The HCU will use these signals to prevent wheel lockup from occurring. Although the exact method the HCU will use to do this will vary between the different ABS systems. the following will occur: - The ECU will determine what wheel is in danger of lockup. This decision is based on the wheel rotation speed and the deceleration rate of the other wheel(s). -The ECU will then send an electrical signal to the HCU. This activates the solenoid that controls the isolation/inlet valve for the hydraulic circuit for that wheel. This action cuts off the fluid flow, preventing any more master cylinder hydraulic pressure from reaching the wheel. -The ECU then looks at the sensor signal from the affected wheel again. -If the affected wheel is still decelerating too quickly, the ECU will send a signal to the HCU that will open the normally closed dump/outlet valve for that circuit. This dumps any applied pressure from the brake back to the reservoir. -Once the affected wheel comes back to a speed whick is acceptable to the ECU, the ECU will return the inlet/isolation and dump/outlet valves back to their normal positions. This allows brake fluid to travel to the brake units once again. -These actions will repeat until the brakes can be applied without risk of lockup. Different traction situations will require more or less cycles of the valves.